The electrical content of automobiles and other useful articles of manufacture is continually increasing, leading to a corresponding increase in the demand for reliable electrical connectors. In the case of automobile connectors many applications require multi-terminal male/female type connectors. Multi-terminal connectors require appreciable force to engage and disengage the connection and it is, of course, important that such connectors be fully and properly engaged.
Many electrical terminals are made of copper alloys that provide good strength and bulk electrical conductivity properties. However, copper alloy terminals oxidize in air, and the resulting oxidized coatings increase the electrical resistance of the connection. Accordingly, it is a common practice to provide a tin, silver or gold coating to the surface of such copper alloy terminals. These metals provide low electrical contact resistance and oxidation protection to the copper alloy terminal, but tin and silver in particular do not have low coefficients of friction and tend to increase the force required to engage and disengage the connectors. While gold has a relatively low coefficient of friction, it is too expensive for many connector applications.
It would be particularly useful to have a tin or silver coating layer for such copper-based connectors that would retain the low contact resistance of the base metal and yet display a lower coefficient of friction for engaging the terminal pieces. There have been suggestions to incorporate low friction polymer particles such as polyimide, polyamide and polytetrafluoroethylene particles with tin or lead particles to form a mixture that can be applied in suitable fashion to the surface of a copper base terminal alloy stock material. These practices are described, for instance, in Guenin, U.S. Pat. No. 5,028,492, "Composite Coating for Electrical Connectors"; Guenin et al, U.S. 5,141,702, "Method of Making Coated Electrical Connectors"; and Endo et al, U.S. Pat. No. 5,235,743, "Method of Manufacturing a Pair of Terminals Having a Low Friction Material on a Mating Surface to Facilitate Connection of the Terminals". The preparation of tin, tin alloy or lead alloy particulate mixtures with particles of a suitable polymer requires separate processing operations. Further operations are required to form a cladable layer of the mixture and adhere the cladding material to the copper base terminal alloy. In one embodiment of the Guenin disclosures, it is proposed to co-deposit polymer particles with tin from a tin sulfate electroplating bath so as to provide an electro-deposited tin layer entraining particles of polyimide, polyamide or polytetrafluoroethylene. In these Guenin disclosures, the thickness of the tin matrix with the polymer dispersion is of the order of about one to about three microns, and the diameter of the polymer particles is from about 0.5 to about 3 microns.
As stated, these co-deposition and/or cladding operations are cumbersome and add to the cost of the terminal manufacture. It would be preferable to have a practice that enables a copper alloy terminal stock or a copper alloy terminal to be simply electroplated with tin in a suitable form and a suitable lubricating material applied to the tin that does not reduce the conductivity of the terminal.